Résumé:
Wetlands are areas with high ecological, economic and social stakes. In the Mediterranean, they have strong specificities and cover (18.5 (± 3.5) million hectares, which corresponds to 1.5% of the world's wetlands. Algeria has more than 1,500 wetlands, 50 of which have already been classified as Ramsar sites, between 1982 and 2011 by the Directorate General of Forests. Their total surface area is estimated at nearly three (03) million hectares (2,991,013.00 ha). In the northwest of the country, the Macta Marshes wetland is located, classified as a specific ecosystem on the west coast of the country, qualifying it to be identified and included in the world list of Ramsar sites of international importance. he objective of this study is to assess its physical, biological, ecological and environmental values. Using the tools of geomatics, we carried out a diachronic diagnosis referring to the reference periods 1958, 2015 and 2020 for the eastern part of the Macta belonging to Mostaganem. The zone covers 37 km2 or 7% of the total surface area of Grande Macta (532.5 km2). The approach used required the exploitation of several multisource data (topographic and thematic maps "1952, 1958, 1985 and 2008", satellite images "2015 to 2020 provided by Landsat-8 and Sentinel-2, NDVI and NDWI, Google Earth Pro (2020), Microsoft Bing (2018), Corine Land Cover data, OpenStreetMap and Ramsar data sheets and field validation). The application of GIS and remote sensing methods produced a 97% valid map from which several indices were managed and analyzed. The analysis showed that between 1958 and 2020 a total surface area of 6.5 km2 or 18% of the total surface area of the site studied (37 km2) was impacted by the spatial and temporal change that occurred in 62 years. Forests and halophilic vegetation are the most impacted, they have lost respectively 3.4 km2 and 3.1 km2. Surface losses have been converted into "free" surface water (3.1 km2), agricultural (1.69 km2) and urbanized (1.7 km2) water. For agriculture, 5.30 km2 of cultivated land and 3.29 km2 of farmland have been converted into irrigated market gardening (greenhouse and open air) and tree orchards (olive and citrus trees). For surface (free) water, the total surface area of temporary water bodies mapped by satellites has decreased from 4.1 km2 in 2015 to 0.9 km2 in 2020, a regression of 3.2 km2 in 5 years, which corresponds to an average annual loss of 0.64 km2 (64 ha/year). This shows that the area and duration of flooding have been reduced. This evolution can be explained by the natural effect mainly related to new climatic conditions and anthropogenic factors linked to agriculture, livestock farming and urbanization. The results obtained therefore provide a current, up-to-date and useful database for management, planning and decision-making to ensure the conservation and preservation of this ecologically balanced environment.
